Willy's Blend - Willy Myco's Official Premium Imported Manure-Based Substrate - 5 lbs
$2999Unit price /Unavailable
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Midwest's Black Cow Manure Substrate & Casing Mix - 30 Pounds (BULK 6-PACK)
$9799$12500Unit price /Unavailable
Why Choose a Manure-Based Substrate?
Manure-based substrates incorporate composted manure (cow, horse, or specialty aged) into a CVG or coir base. The manure contributes additional nitrogen, micronutrients, and beneficial microbes that pure CVG doesn't have — which translates to faster colonization, stronger pinning, and often larger total yields.
The tradeoff: manure-based substrates are more sensitive to processing and storage than pure CVG. Manure is harder to consistently pasteurize, and if anything goes wrong in handling, the nutrient-rich substrate can become a breeding ground for contamination. For experienced growers who manage their grows carefully, the yield benefits are real. For brand-new growers, the simplicity of pure CVG is usually the smarter starting point.
If you've done a few successful grows on Midwest's Select and want to see what manure-based substrates can do, this collection is the next step.
The Manure-Based Lineup
Black Cow Manure Casing Mix — The Classic Standard
Best for: Growers who want to step up from pure CVG to a proven manure-based blend without going premium.
Our original manure-based substrate, blending composted black cow manure into a CVG base. It's been the reliable mid-tier option since long before the premium imports arrived — still a popular seller for growers who want manure-based performance at a reasonable price.
Available in 5 lb bags for individual grows or as a 30 lb 6-pack at a per-bag discount for multi-tub workflows.
Willy's Blend — Premium Imported
Best for: Growers who want the highest-quality manure-based substrate available, no compromises.
Willy's Blend is a collaboration between Midwest Grow Kits and YouTube content creator Willy Myco. We import the base ingredients to produce this premium blend at our facility, then pasteurize and bag it like our other substrates. It's positioned as a step up from Black Cow for growers willing to pay more for noticeably higher-quality inputs.
If you've heard about Willy's Blend on YouTube and wondered where to get it — this is the official source.
Wild Horse Manure Booster — The Secret Weapon
Best for: Growers who want to enhance an existing substrate (CVG or manure-based) with a unique nutrient boost.
The Wild Horse Manure Booster is unlike anything else in our lineup. We work with a partner ranch in Wyoming that sends us genuine wild horse manure, which we process and bring to field capacity with a few additional ingredients. It comes as a 1 lb add-on product — you mix one bag per 10 lbs of substrate to enhance the nutrient profile of your grow.
Wild horse manure is different from domestic cow or horse manure. The free-ranging diet (varied grasses, herbs, browse) produces manure with a more diverse micronutrient profile, and many experienced growers swear by it for noticeably better results. It's a relatively small SKU but has a devoted following.
Grass Lover's Premium — For Grass-Loving Species
Best for: Growers cultivating grass-loving species, particularly those following GordoTek's techniques.
Our Grass Lover's Premium uses a different aged manure mixed with straw, designed for grass-loving species rather than the typical cubensis-style cultivars. It was developed in partnership with content creator GordoTek and his Patreon community, and works particularly well with the bulk-growing techniques he's popularized.
Available as a 3 lb substrate bag, or as part of our complete Grass Lover's Kits if you want substrate plus the full setup.
Grass Lover's XL Refill Kit
Best for: Existing owners of the Complete XL Specialty Grass Lover's Kit who need to restock.
The XL Refill Kit includes the substrate and supplies you need to run another grow in your existing Grass Lover's XL Kit setup. Much more economical than buying a whole new kit each cycle.
How to Use Manure-Based Substrate
Manure-based substrates use the same bulk grow workflow as pure CVG. The basic steps:
- Mix your colonized grain spawn with the manure-based substrate at roughly a 1:3 ratio
- Pack the mixture into a clean monotub
- Colonize at room temperature with air holes sealed (typically 7 to 14 days)
- Fruit by opening air holes and introducing light and fresh air exchange
- Harvest when mushrooms mature, then mist for the next flush
New to bulk growing? Our Step-by-Step Bulk Monotub Grow Guide covers every step with photos — from prepping your tub through harvesting multiple flushes. The same workflow applies whether you're using CVG or a manure-based substrate.
How much manure-based substrate do I need for my monotub?
- 28Q small monotub: 4 lbs of bulk substrate paired with one spawn bag, or use a 32oz grain jar with no extra substrate needed
- 44Q medium monotub: 7.5 lbs of bulk substrate paired with one spawn bag (2.25 to 2.5 lbs)
- 66Q large monotub: 10 lbs of bulk substrate paired with two spawn bags (5 lbs total)
Note: a single 5 lb Black Cow or Willy's Blend bag is sized for a 28Q small or a 44Q medium with a top-off from another bag. For a 66Q large, two 5 lb bags or the 30 lb 6-pack works well.
Why our manure-based substrates work
- Pasteurized in our dedicated 1200L Blue Myco autoclave at 160°F for 3 to 4 hours — the right process for manure-based substrates, leaving beneficial microbes intact while killing harmful contaminants.
- Made fresh daily in-house. No inventory sitting on shelves; the substrate you receive was made recently.
- Hydrated to field capacity. No water to add; ready to mix with spawn immediately.
- Unique sourcing. Willy's Blend uses imported premium base ingredients. Wild Horse Booster comes from a partner ranch in Wyoming. Grass Lover's is developed in partnership with GordoTek and his Patreon community.
A note on contamination risk
Manure-based substrates are more sensitive to contamination than pure CVG. This isn't a flaw in the product — it's a function of nutrient density. Richer substrates feed your mycelium faster, but if anything goes wrong (poor sterile technique during spawn-out, an under-colonized grain bag, a torn liner) the same nutrient density that feeds your mushrooms also feeds molds and bacteria.
The practical advice: use manure-based substrates when you've already got good sterile technique dialed in. Mix spawn and substrate in a clean environment (ideally in a flow hood or still air box), and don't introduce them to a monotub that hasn't been thoroughly sanitized. If you've been struggling with contamination on pure CVG, that's a sign to fix your technique before stepping up to richer substrates.
Quick decision tree
- First manure-based substrate? Start with Black Cow — affordable, proven, time-tested.
- Want the premium tier? Willy's Blend — the highest-quality manure-based substrate in our lineup.
- Want to enhance whatever you're already running? Add a Wild Horse Manure Booster (1 bag per 10 lbs).
- Growing grass-loving species (or following GordoTek's techniques)? Grass Lover's Premium.
- Already own the Grass Lover's XL Kit? Grab the XL Refill Kit.
Frequently Asked Questions About Manure-Based Substrate
What is manure-based substrate and how is it different from CVG?
Manure-based substrate incorporates composted manure (cow, horse, or specialty aged) into a CVG or coir base. The manure adds nitrogen, micronutrients, and beneficial microbes that pure CVG doesn't have, which can translate to faster colonization and larger yields. The tradeoff is higher contamination risk if anything in your process isn't dialed in.
Should I start with CVG or a manure-based substrate?
Start with pure CVG (our Midwest's Select Bulk Substrate) for your first few bulk grows. CVG is cleaner, more predictable, and forgives more beginner mistakes. Once you've completed a few successful grows and have your technique dialed in, manure-based substrates like Black Cow or Willy's Blend can deliver better results.
What's the difference between Black Cow and Willy's Blend?
Black Cow is our original manure-based substrate — a reliable, time-tested blend using composted cow manure at an accessible price. Willy's Blend is the premium tier, created in collaboration with YouTube content creator Willy Myco using imported high-quality base ingredients. Both are pasteurized identically and work the same way; Willy's Blend is for growers who want the highest-quality manure-based option available.
What is the Wild Horse Manure Booster and how do I use it?
The Wild Horse Manure Booster is a 1 lb additive sourced from a partner ranch in Wyoming. Wild horse manure has a more diverse micronutrient profile than typical domestic livestock manure because the horses eat varied wild forage. You mix one bag per 10 lbs of substrate to enhance the nutrient profile of any grow. It works with both CVG and manure-based substrates.
What's the Grass Lover's substrate for?
Grass Lover's Premium uses a different aged manure mixed with straw, designed for grass-loving species (not the typical cubensis-style cultivars). It was developed in partnership with content creator GordoTek and his Patreon community, and works particularly well with the techniques he's popularized. It's a niche product but the right choice for growers in that community.
How are your manure-based substrates processed?
Every bag is made fresh in-house and pasteurized in our dedicated 1200L Blue Myco autoclave at 160°F for 3 to 4 hours. Pasteurization (rather than full sterilization) is the right process for manure-based substrates because it kills harmful contaminants while leaving beneficial microbes intact, creating a competitive environment that helps prevent contamination during fruiting.
Are manure-based substrates more likely to get contaminated?
They have higher contamination risk than pure CVG when something in your process goes wrong, because the nutrient density that feeds your mycelium also feeds molds and bacteria. They're not inherently contaminated — we pasteurize them carefully — but they're less forgiving of mistakes in spawn-out technique, monotub sanitation, or grain spawn quality. Master CVG grows first, then graduate to manure-based.
How much manure-based substrate do I need for my monotub?
For a 28Q small monotub, 4 lbs of bulk substrate paired with one spawn bag, or use a 32oz grain jar with no extra substrate needed. For a 44Q medium monotub, 7.5 lbs paired with one spawn bag. For a 66Q large monotub, 10 lbs paired with two spawn bags. A single 5 lb Black Cow or Willy's Blend bag covers a 28Q small; multiple bags or the 30 lb 6-pack covers larger tubs.
Can I mix Wild Horse Booster with Willy's Blend or Black Cow?
Yes. The Wild Horse Manure Booster is designed to work with any base substrate — CVG, Black Cow, Willy's Blend, or anything else. Mix one 1 lb bag per 10 lbs of base substrate. The micronutrient diversity of wild horse manure complements the nutrient profile of the base substrate rather than duplicating it.
Do I need to add water to manure-based substrate bags?
No. Every bag is hydrated to field capacity (the optimal moisture level for mushroom colonization) before it leaves our facility. Mix directly with your colonized grain spawn. Adding water typically results in over-hydration and contamination risk.
How long do manure-based substrate bags last?
Pasteurized substrate bags are best used within 60 to 90 days of production for optimal performance. Refrigerated storage extends that window. We make substrate fresh daily and ship the freshest stock first, so the bag you receive will typically be just days old.